1. Field of the Invention
The present invention relates to a method of measuring the temperature of an electrical storage device, and particularly relates to an electrical storage device temperature measuring method for accurately measuring the internal temperature of an electrical storage device.
2. Description of the Related Art
Electrical storage devices such as a lithium ion secondary battery and an electric double layer capacitor have been used for various applications, and have been widely applied to, for example, battery packs for mobile phones, batteries for PCs, and batteries for vehicles. In such a case, it is a very important matter to detect a state of an electrical storage device such as a deterioration state (SOH; state of health) or a remaining capacity (SOC; state of charge). In particular, with regard to a vehicle, detection of the state of an electrical storage device in an energy-conservation vehicle performing an idling stop, a hybrid vehicle, an electric vehicle, or the like is deeply associated with travelling of the vehicle and thus is drawing attention as being very important.
In a generally well-known method for detecting the state of the electrical storage device, the voltage, the current, and the temperature of the electrical storage device are measured to calculate the deterioration state (SOH), the remaining capacity (SOC), or the like of the electrical storage device. In the method, the temperature of the electrical storage device is an important measurement parameter since it has a great effect on deterioration of the electrical storage device.
As the related art of a method of measuring the temperature of an electrical storage device, a method is generally known in which a temperature detection element is put on or connected to the electrical storage device to directly measure the temperature as in Japanese Unexamined Patent Application Publication No. 6-260215. Japanese Unexamined Patent Application Publication No. 6-260215 states that a Zener diode is used as the temperature detection element and connected to a plus terminal of the electrical storage device, whereby the temperature transmitted from the plus terminal of the electrical storage device can be accurately measured. However, in Japanese Unexamined Patent Application Publication No. 6-260215 (related art example 1), due to self-heating of an internal resistor of the electrical storage device or the like, a great difference may be produced between the temperature of a temperature detection point of the temperature detection element (the plus terminal of the electrical storage device in the related art example 1) and the internal temperature of the electrical storage device, and thus the temperature of the electrical storage device cannot be accurately recognized.
Meanwhile, an apparatus that detects the temperature of an electrical storage device by a temperature detection element such as a thermocouple, obtains the internal impedance of the electrical storage device, and determines a deterioration state (SOH) of the electrical storage device (e.g., see Japanese Unexamined Patent Application Publication No. 2010-67502), and an apparatus that obtains the internal impedance of an electrical storage device without using a temperature detection element and determines the internal temperature of the electrical storage device (e.g., see International Publication No. WO01/16614), have been proposed.
According to Japanese Unexamined Patent Application Publication No. 2010-67502 (related art example 2), the apparatus includes a temperature adjustment means for adjusting the temperature of the electrical storage device, an impedance calculation means for calculating the internal impedance of the electrical storage device, and a deterioration determination means for determining the deterioration state of the electrical storage device on the basis of the calculated internal impedance. In a state where the electrical storage device is adjusted to a temperature within a predetermined range by the temperature adjustment means, on the basis of the voltage of the electrical storage device, and the temperature of the electrical storage device, and a value of the internal impedance calculated when the electrical storage device is charged or discharged with an alternating current of a predetermined frequency (not lower than 10 Hz and not higher than 1 kHz), the deterioration state can be determined by referring to a map of internal impedances that are set so as to be associated with temperatures of the electrical storage device and voltages of the electrical storage device.
In addition, according to International Publication No. WO01/16614 (related art example 3), the apparatus for determining the internal temperature includes an electrical excitation circuit for providing time-varying electrical excitation to the electrical storage device, a response detection circuit for detecting a time-varying electrical response to the electrical excitation, and a calculation circuit for determining the internal temperature by using voltage and current signals derived from the inputted excitation and the response signal. Time-varying electrical excitation is provided in different frequencies (5 Hz, 70 Hz, and 1 kHz in the example), the measured impedance is assigned to an equivalent circuit, and the internal temperature of the electrical storage device is calculated from a specific element value of the equivalent circuit.
However, in the related art example 2, the internal impedance is measured in a low frequency (not lower than 10 Hz and not higher than 1 kHz in the related art example 2) which is influenced by the behavior of ions in an electrolyte of the electrical storage device. Thus, for accurately measuring the internal impedance, the measurement is conducted in a state where the electrical storage device is adjusted to a temperature within the predetermined range by the temperature adjustment means, in order to not be influenced by temperature. In this method, even when it is attempted to estimate the internal temperature of the electrical storage device on the basis of the measurement of the internal impedance, a measured value of the measured internal impedance is different depending on the deterioration state of the electrical storage device. Thus, the internal temperature of the electrical storage device cannot be accurately obtained.
In addition, in the related art example 3, it is suitable to use, for the measurement, a frequency that is less changed with respect to a remaining capacity (SOC). However, similarly to the related art example 2, the internal impedance is measured in a low frequency (5 Hz, 70 Hz, and 1 kHz in the related art example 3) which is influenced by the behavior of ions in an electrolyte of the electrical storage device. Thus, a measured value of the measured internal impedance is different depending on the deterioration state of the electrical storage device, and the internal temperature of the electrical storage device cannot be accurately obtained.